RGBCube/serenity
1
Fork 0
mirror of https://github.com/RGBCube/serenity synced 2025-07-26 01:47:34 +00:00
Code Issues Activity Actions

Kernel: Implement lazy committed page allocation

Browse source 
By designating a committed page pool we can guarantee to have physical
pages available for lazy allocation in mappings. However, when forking
we will overcommit. The assumption is that worst-case it's better for
the fork to die due to insufficient physical memory on COW access than
the parent that created the region. If a fork wants to ensure that all
memory is available (trigger a commit) then it can use madvise.

This also means that fork now can gracefully fail if we don't have
enough physical pages available.
This commit is contained in:
Tom 2020-09-04 21:12:25 -06:00 • committed by Andreas Kling
parent e21cc4cff6
commit b2a52f6208
20 changed files with 329 additions and 67 deletions
Download patch file Download diff file Expand all files Collapse all files

14
Kernel/VM/MemoryManager.h
View file

@ -110,6 +110,9 @@ public:
Yes
};
bool commit_user_physical_pages(size_t);
void uncommit_user_physical_pages(size_t);
NonnullRefPtr<PhysicalPage> allocate_committed_user_physical_page(ShouldZeroFill = ShouldZeroFill::Yes);
RefPtr<PhysicalPage> allocate_user_physical_page(ShouldZeroFill = ShouldZeroFill::Yes, bool* did_purge = nullptr);
RefPtr<PhysicalPage> allocate_supervisor_physical_page();
NonnullRefPtrVector<PhysicalPage> allocate_contiguous_supervisor_physical_pages(size_t size);
@ -155,6 +158,7 @@ public:
void dump_kernel_regions();
PhysicalPage& shared_zero_page() { return *m_shared_zero_page; }
PhysicalPage& lazy_committed_page() { return *m_lazy_committed_page; }
PageDirectory& kernel_page_directory() { return *m_kernel_page_directory; }
@ -185,7 +189,7 @@ private:
static Region* find_region_from_vaddr(VirtualAddress);
RefPtr<PhysicalPage> find_free_user_physical_page();
RefPtr<PhysicalPage> find_free_user_physical_page(bool);
u8* quickmap_page(PhysicalPage&);
void unquickmap_page();
@ -200,9 +204,12 @@ private:
RefPtr<PhysicalPage> m_low_page_table;
RefPtr<PhysicalPage> m_shared_zero_page;
RefPtr<PhysicalPage> m_lazy_committed_page;
unsigned m_user_physical_pages { 0 };
unsigned m_user_physical_pages_used { 0 };
unsigned m_user_physical_pages_committed { 0 };
unsigned m_user_physical_pages_uncommitted { 0 };
unsigned m_super_physical_pages { 0 };
unsigned m_super_physical_pages_used { 0 };
@ -250,4 +257,9 @@ inline bool PhysicalPage::is_shared_zero_page() const
return this == &MM.shared_zero_page();
}
inline bool PhysicalPage::is_lazy_committed_page() const
{
return this == &MM.lazy_committed_page();
}
}